The present invention relates to a valve device, in particular a valve device which can be used in a unit for unloading loose material from a dispenser device to a user unit.
The device disclosed can be used in particular in the chemical and/or pharmaceutical industry and in all cases for unloading containers of loose material consisting of powders, granulated material, pellets, tablets, capsules or similar products.
Such containers are normally emptied at an unloading station and the material they contain is transferred to a collection tank connected, for example, to a user unit or machine which uses the loose material for subsequent processing.
In the above-mentioned unloading station, a supporting structure holds the collection tank at a level lower than that of the container, to allow container emptying by gravity.
Connecting means are used to transfer the material from the container to the tank, said connecting means consisting, for example, of a rigid cylindrical tube with a vertical axis, supporting an interchangeable tubular bag in which the loose material being processed flows.
Such connections must be substantially airtight, so that, as the powdered material passes through the tubular bag, the diffusion of powders in the surrounding environment is kept within extremely narrow limits.
The importance of the problem mentioned above increases when the substances handled are chemical substances or compounds that are not easily degradable in the environment and in some cases potentially toxic or harmful.
Moreover, obviously when switching from processing one material to processing another, the tubular bag must be substituted and the connection thoroughly cleaned.
At its upper end, the cylindrical tube normally has a ring-shaped body, or spacer, designed for connection to the container and airtight fixing of the upper end of the tubular bag. The lower outfeed end of the container is also fitted with a valve element designed to open or close the lower end.
Said valve element normally consists of a butterfly valve with a flat disk-shaped shutter element that rotates in both directions about a horizontal axis between a position in which the lower end of the container is closed, with the shutter lying in a substantially horizontal plane, and a position in which the lower end of the container is open, with the shutter lying in a substantially vertical plane, allowing the material to be unloaded from the container to the cylindrical tube.
Conventional unloading units, of the type described, are not fully satisfactory as regards the problems relative to pollution. They have the disadvantage that, during container emptying, the face of the disk-shaped element which faces the outside environment when the valve element is closed makes contact with the powdered material during unloading, when the disk-shaped element is in the vertical position.
Secondly, during removal of the container from the cylindrical tube, the upper end of the spacer, having also been in contact with the powdered material, is exposed to the surrounding environment.
Attempts were made to overcome the above-mentioned disadvantages with a solution that involved inserting a hopper of a substantially known type between the valve element of the container and the above-mentioned spacer connected to the tubular pipe, equipping the spacer with a butterfly valve so as to form a washing chamber between the inner surface of the hopper, the lower surface of the container outfeed valve and the upper surface of the valve located substantially at the spacer infeed. Moreover, in said case, the hopper must be suitably modified and equipped with internal washing nozzles.
When the loose material has been unloaded, the container valve and the spacer valve are closed and, before the container is separated from the pipe and from the spacer, the inside of the hopper is washed.
Said washing is carried out using directional nozzles giving onto the inner surface of the hopper, to clean the surfaces of the two valves which will be in contact with the outside environment.
However, the solution just described is not without disadvantages, which are mainly due to the considerable dimensions of the washing chamber, which make thorough washing of it difficult.
Moreover, the use of nozzles located on the side surface of the hopper does not guarantee thorough cleaning of the valves and in particular their central zone.
To overcome the problems relative to environmental pollution with reference to the normal unloading devices described above, another solution was developed, described in EP 1.043.252.
Said solution relates to an unloading unit in which the valve element for closing the container consists not of the above-mentioned single disk-shaped element, but of two disk-shaped closing elements positioned one over the other and releasably connected to one another.
More precisely, said valve element behaves for all practical purposes, as regards opening and closing operations, like the devices described above but, at the moment when the container is substituted, the above-mentioned closing elements positioned one over the other are detached from one another and whilst the first closes the outfeed end of the empty container, the second closes the upper end of the spacer, preventing contact between the above-mentioned contaminated parts and the outside environment, towards which the faces that were previously in contact with one another face.
In the case of said valve element, before the two closing elements are separated, they may be washed to eliminate powder residues that are inevitably deposited in the circular ring formed by the two closing elements.
To facilitate washing of such devices, versions were developed equipped with detachment means substantially designed to noticeably move the closing elements away from one another so that they leave an air space between them which promotes cleaning before definitive separation.
The latter devices are also not without disadvantages.
Firstly, the production of closing elements which fit together perfectly requires high precision mechanical machining involving operating difficulties and high costs.
Moreover, a device made in that way requires constant and extended periodic maintenance since it is so complex that it needs continuous attention. The result of this is periodic, inconvenient, inevitable system downtime.
Due to its complex construction, the device just described also has surfaces that hold onto the powders at the end of unloading which have a substantially irregular shape and, therefore, are difficult to wash.
Even when an air space is created between the two closing elements, the washing space remains limited and, as a result, cleaning is not thorough enough, since the action of the detergent fluids, normally dispensed by spray nozzles of the known type, is not effective enough.